The Administrator has to activate this by clicking Settings → CRM → Fields → Order & opportunities: 
Users can then choose their own probability of an opportunity:
Articles in this section
- Upselling in Subscriptions in Upsales
- Weekly pipeline commit
- Q: How do users choose the probability for an opportunity stage?
- Sales process BASIC
- How to use won/lost buttons with Opportunities
- Competitors overview
- Solution-focused selling
- 3 steps to the right timing
- Sales process guide: Reasons to verify your lead's budget
- How to define stakeholders & job titles in the Sales process